PNNL

Abstract

Long-term patterns in river water temperature are relevant to questions pertaining to fish welfare and hydroelectric dam operations. Yet, in fish biology and watershed hydrology, the typical ways in which river water temperature data are displayed do not readily and easily show the long-term patterns in the data. We use different styles of displaying such data so that changes of river water temperature over time can readily be seen from various perspectives. One such approach is to display the fourth dimension, time, split into two dimensions, with water temperature data shown as a three dimensional response surface that is color-coded according to various levels of temperature. This includes a version that shows long term patterns at levels above a threshold which is significant for the welfare of some fish species. For example, at Bonneville Dam, Oregon, along the Lower Columbia River, the average daily water temperature from USGS sources for 62 years, from 1938 to 1999, shows an increasing pattern, from mid-July to mid-September, in the number of days exceeding 21 C, a critical level for some salmonids.